1. Technical Field of the Invention
The present invention relates to a method of electroless gold plating and a gold plate coated material.
2. Description of the Related Art
Heretofore, as a method of forming a gold plate layer on a surface of an electrical contact material such as used for connectors, switches or printed wiring boards, there has been known a method of performing electroless substitution gold plating on a surface of a metallic base material.
However, such a method of forming a gold plate layer by means of electroless substitution gold plating may involve problems as below. That is, when the electroless substitution gold plating is performed, the metallic base material as a material to be plated with gold may locally dissolve to generate micro recesses at the surface of the metallic base material. The micro recesses thus generated will cause poor deposition of gold, so that pinholes may occur at the surface of the gold plate layer to be formed. This may lead to problems in that the obtained electrical contact material deteriorates in its corrosion resistance and conductivity and delamination occurs at an interface with solder when the electrical contact material is connected with another component by soldering.
On the other hand, in order to solve such problems due to pinholes, there may be used a method of further performing electroless reduction gold plating on the gold plate layer formed by the electroless substitution gold plating thereby to cover the pinholes. In this method, however, the gold plate layer may have to be formed with a large thickness in total to allow the electroless reduction gold plating to cover the pinholes, which may be problematic in cost.
In view of the above, Patent Document 1 (Japanese Patent Application Publication No. 2005-54267) discloses a method of performing palladium plating to form a palladium plate layer on a base material and thereafter forming a gold plate layer on the palladium plate layer by means of electroless reduction gold plating.